Pigment loaded ink is relatively new in industrial printing used for its advantages such as being environmentally friendly, durable, rapidly drying, non-fading and having low bleeding tendencies.
Pigmented ink, however, may also require special handling. Pigments, being solid particles, tend to settle and aggregate which may lead to packing of the sediments. This can have a great impact on the quality of the finished product (concentration gradients, blocking of the jet leading to inconsistency of the color, etc.). For example, white ink containing Titanium Oxide (TiO2) is the most widely used white pigment because of its brightness and very high refractive index. However, TiO2 may have a high sedimentation rate, which in some cases, for example may be 10-20 mg/hour.
In the glass-printing industry, special ink compositions are used for long lasting glass printing, which commonly include micro and/or nano-particles of glass or ceramics (frits), wherein the fixation of the printed image is by firing the printed glass in a furnace at high temperatures of 550° C. and more. The exposure of the ink to such high temperatures causes the glass micro particles to melt, thus affixing the ink pigments into the printed glass surface.
Traditionally, industrial large format printing on substrates such as paper, glass, stone and others was performed using screen-printing and smearing of the ink over the screen. Currently, printing technology is shifting to digital inkjet printing to reduce costs, eliminating screen and film storage space and improve yield, consistency and time to market.
However, printheads include ink conducting channels having micro-scale diameters and an ink delivery mechanism based on pressure gradients and capillarity highly sensitive to clogging and packing by debris and ink drying. Employing pigmented ink and in some cases a mixture of pigment and frits in the inkjet printing environment poses a challenge since it may bring about aggregation and sedimentation of the pigment particles and, in some cases frits, in the ink delivery and circulation tubes as well as packing of the sediments in the tubes and printhead nozzles.
For the reasons discussed above printing with pigmented ink and especially ceramic ink, i.e., pigmented ink mixed with glass or ceramic micro and/or nano-particles, cannot be carried out with a standard inkjet printhead and the printhead needs to be adapted so that to allow smooth operation with a minimum of ink settling and aggregating and/or packing of the sediments.
The common inkjet printhead spatial calibration process currently practiced in printers employing more than one printhead in the printing run involves individually calibrating each printhead relative to a bracket, which in turn is connected to an insert using registration pins and registration holes. The insert is then connected to a printer, e.g., mounted on a reciprocating carriage or static bridge. This three-step process allows for a cumulative error in the printheads spatial calibration.